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NVAEasyJEE 2023Oxidation States & Ionisation Energies

JEE Chemistry 2023 Question with Solution

In chromyl chloride, the oxidation state of chromium is (+)(+) \hspace{2cm}.

Answer

Correct answer:6

Step-by-step solution

Standard Method

Given: chromyl chloride.

Find: the oxidation state of chromium.

Step 1: Write the formula of chromyl chloride.

Chromyl chloride has the molecular formula:

CrO2Cl2\mathrm{CrO_2Cl_2}

Step 2: Assign oxidation states to known elements.

Oxygen generally has oxidation state −2-2.

Chlorine generally has oxidation state −1-1.

Step 3: Let the oxidation state of chromium be xx.

The sum of oxidation states in a neutral molecule is zero.

x+2(−2)+2(−1)=0x + 2(-2) + 2(-1) = 0

Step 4: Solve for xx.

x−4−2=0x - 4 - 2 = 0 x=+6x = +6

Step 5: Final Answer.

The oxidation state of chromium in chromyl chloride is +6+6.

Quick Tip

In chromyl chloride (CrO2Cl2)\left(\mathrm{CrO_2Cl_2}\right), chromium shows its highest common oxidation state, which is also observed in dichromates and chromates.

Common mistakes

  • Taking chlorine as positive here is incorrect because in chromyl chloride chlorine is present as chloride and generally has oxidation state −1-1. Assign −1-1 to each chlorine before solving.

  • Forgetting that the molecule is neutral is incorrect because the total oxidation state sum must be 00, not a nonzero value. Set up the equation so that all oxidation numbers add to zero.

  • Using oxygen as −1-1 instead of −2-2 is incorrect because there is no peroxide linkage here. Use oxygen as −2-2 in CrO2Cl2\mathrm{CrO_2Cl_2}.

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